16,480 research outputs found
The evolution of the self-lensing binary KOI-3278: evidence of extra energy sources during CE evolution
Post-common-envelope binaries (PCEBs) have been frequently used to
observationally constrain models of close-compact-binary evolution, in
particular common-envelope (CE) evolution. However, recent surveys have
detected PCEBs consisting of a white dwarf (WD) exclusively with an M dwarf
companion. Thus, we have been essentially blind with respect to PCEBs with more
massive companions. Recently, the second PCEB consisting of a WD and a G-type
companion, the spectacularly self-lensing binary KOI-3278, has been identified.
This system is different from typical PCEBs not only because of the G-type
companion, but also because of its long orbital period. Here we investigate
whether the existence of KOI-3278 provides new observational constraints on
theories of CE evolution. We reconstruct its evolutionary history and predict
its future using BSE, clarifying the proper use of the binding energy parameter
in this code. We find that a small amount of recombination energy, or any other
source of extra energy, is required to reconstruct the evolutionary history of
KOI-3278. Using BSE we derive progenitor system parameters of M1,i = 2.450
Msun, M2,i = 1.034 Msun, and Porb,i ~ 1300 d. We also find that in ~9 Gyr the
system will go through a second CE phase leaving behind a double WD, consisting
of a C/O WD and a He WD with masses of 0.636 Msun and 0.332 Msun, respectively.
After IK Peg, KOI-3278 is the second PCEB that clearly requires an extra source
of energy, beyond that of orbital energy, to contribute to the CE ejection.
Both systems are special in that they have long orbital periods and massive
secondaries. This may also indicate that the CE efficiency increases with
secondary mass.Comment: Accepted for publication in A&A Letters, 4 pages, 2 figure
Persistence in fluctuating environments
Understanding under what conditions interacting populations, whether they be
plants, animals, or viral particles, coexist is a question of theoretical and
practical importance in population biology. Both biotic interactions and
environmental fluctuations are key factors that can facilitate or disrupt
coexistence. To better understand this interplay between these deterministic
and stochastic forces, we develop a mathematical theory extending the nonlinear
theory of permanence for deterministic systems to stochastic difference and
differential equations. Our condition for coexistence requires that there is a
fixed set of weights associated with the interacting populations and this
weighted combination of populations' invasion rates is positive for any
(ergodic) stationary distribution associated with a subcollection of
populations. Here, an invasion rate corresponds to an average per-capita growth
rate along a stationary distribution. When this condition holds and there is
sufficient noise in the system, we show that the populations approach a unique
positive stationary distribution. Moreover, we show that our coexistence
criterion is robust to small perturbations of the model functions. Using this
theory, we illustrate that (i) environmental noise enhances or inhibits
coexistence in communities with rock-paper-scissor dynamics depending on
correlations between interspecific demographic rates, (ii) stochastic variation
in mortality rates has no effect on the coexistence criteria for discrete-time
Lotka-Volterra communities, and (iii) random forcing can promote genetic
diversity in the presence of exploitative interactions.Comment: 25 page
From Loop Groups to 2-Groups
We describe an interesting relation between Lie 2-algebras, the Kac-Moody
central extensions of loop groups, and the group String(n). A Lie 2-algebra is
a categorified version of a Lie algebra where the Jacobi identity holds up to a
natural isomorphism called the "Jacobiator". Similarly, a Lie 2-group is a
categorified version of a Lie group. If G is a simply-connected compact simple
Lie group, there is a 1-parameter family of Lie 2-algebras g_k each having
Lie(G) as its Lie algebra of objects, but with a Jacobiator built from the
canonical 3-form on G. There appears to be no Lie 2-group having g_k as its Lie
2-algebra, except when k = 0. Here, however, we construct for integral k an
infinite-dimensional Lie 2-group whose Lie 2-algebra is equivalent to g_k. The
objects of this 2-group are based paths in G, while the automorphisms of any
object form the level-k Kac-Moody central extension of the loop group of G.
This 2-group is closely related to the kth power of the canonical gerbe over G.
Its nerve gives a topological group that is an extension of G by K(Z,2). When k
= +-1, this topological group can also be obtained by killing the third
homotopy group of G. Thus, when G = Spin(n), it is none other than String(n).Comment: 40 page
Dynamical Quasicondensation of Hard-Core Bosons at Finite Momenta
Long-range order in quantum many-body systems is usually associated with
equilibrium situations. Here, we experimentally investigate the
quasicondensation of strongly-interacting bosons at finite momenta in a
far-from-equilibrium case. We prepare an inhomogeneous initial state consisting
of one-dimensional Mott insulators in the center of otherwise empty
one-dimensional chains in an optical lattice with a lattice constant . After
suddenly quenching the trapping potential to zero, we observe the onset of
coherence in spontaneously forming quasicondensates in the lattice. Remarkably,
the emerging phase order differs from the ground-state order and is
characterized by peaks at finite momenta in the
momentum distribution function.Comment: See also Viewpoint: Emerging Quantum Order in an Expanding Gas,
Physics 8, 99 (2015
The Dwarf Nova Outbursts of Nova Her 1960 (=V446 Her)
V446 Her is the best example of an old nova which has developed dwarf nova
eruptions in the post-nova state. We report on observed properties of the
long-term light curve of V446 Her, using photometry over 19 years. Yearly
averages of the outburst magnitudes shows a decline of ~0.013 mag/yr,
consistent with the decline of other post-novae that do not have dwarf nova
outbursts. Previous suggestions of bimodal distributions of the amplitudes and
widths of the outbursts are confirmed. The outbursts occur at a mean spacing of
18 days but the range of spacings is large (13-30 days). From simulations of
dwarf nova outbursts it has been predicted that the outburst spacing in V446
Her will increase as M-dot from the red dwarf companion slowly falls following
the nova; however the large intrinsic scatter in the spacings serves to hide
any evidence of this effect. We do find a systematic change in the outburst
pattern in which the brighter, wider type of outbursts disappeared after late
2003, and this phenomenon is suggested to be due to falling M-dot following the
nova.Comment: To appear at the Astronomical Journal; 7 pages, 1 table, 11 figure
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Animals bearing malignant grafts reject normal grafts that express through gene transfer the same antigen.
Breaking the state of immunological unresponsiveness of tumor-bearing individuals to cancer is a prerequisite for active or passive tumor-specific immunotherapy. To study this problem the immunogenic MHC class I antigen, K216 was transfected into a progressor tumor. The transfected tumors were regularly rejected by normal mice but grew progressively in mice bearing nontransfected tumors. In addition, transgenic mice were derived to obtain normal cells and tissues expressing the same K216 gene product. Normal mice rejected K216-positive normal or malignant tissue grafts and generated K216-specific CTL in vitro and in vivo in response to these challenges. In contrast, mice bearing nontransfected tumors, though rejecting K216-positive nonmalignant tissue grafts, did not reject K216-positive tumors nor generate K216-specific CTL in response to K216-positive tumor cells. Mice bearing K216-positive tumors also rejected the nonmalignant K216-positive tissue grafts, but this in vivo response failed to lead to rejection of the simultaneously present tumor graft expressing the same antigen; in fact, immunity had no measurable effect whatsoever on tumor size or incidence and caused no selection for antigen loss variants. Taken together, the present findings suggest that transfer of expression of a target antigen into nonmalignant cells provides a way for obtaining effective stimulation of antigen-specific CTL in tumor-bearing mice, but that additional manipulations will be required to cause immunological rejection of established tumors
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